定语从句（3）从句的本质
从句的本质是：句子作成分/词类
在简单句中，成分都是由单词或短语充当的：
I know you.
主语是I ；谓语是know ；宾语是you
I enjoy reading novels.
主语是I ；谓语是know ；宾语是reading novels（动宾短语）
I know he is ill.
主语是I ；谓语是know ；宾语是he is ill（句子）我们可以看出：最后的句子He is ill 是作了句子成分的，作宾语，因此可以叫它为“宾语从句”
从另一个角度来说：这个句子相当于一个名词，因此可以叫做“名词性从句”
That she finished reading an English novel surprised us all.
上面的句子当中，句子She finished reading an English novel作了主语，因此叫“主语从句”，也相当于名词，还可以叫做“名词性从句”
She finished reading an Englishnovel yesterday. She finished reading an Englishnovel at the age of 12.
She finished reading an Englishnovel when she was 12.
从上面的变化情况我们可以看出，从单词作成分，短语作成分到句子作成分，作的都是状语，因此从句叫“状语从句”，或叫“副词性从句”。

The little girl finished reading an English novel. The girl in school uniform finished reading an English novel.
The girl who is 12 finished reading an English novel.从上面的变化情况我们可以看出，从单词作成分，短语作成分到句子作成分，作的都是定语，因此从句叫“定语从句”，或叫“形容词性从句”。